Electric Circuits & Electrical Safety (Cambridge (CIE) IGCSE Physics)

Fig. 10.1 shows an arrangement for making an electromagnet.

(i) State a material which is suitable for the core of the electromagnet.

[1]

(ii) State the name for component X in Fig. 10.1.

 [1]

(iii) Describe and explain how component X varies the strength of the electromagnet.

 [2]

The switch is closed. The reading on the ammeter is 1.5 A.

Calculate the resistance of the circuit.

resistance = .................................................... Ω 

A student does an experiment to determine the resistance of a fixed resistor, R.

The student draws an incomplete diagram of the circuit, as shown in Fig. 10.1.

(i) On Fig. 10.1, draw the missing circuit symbols.

[3]

(ii) Describe how the student could use the circuit to determine a reliable value for the resistance of R.

[5]

Fig. 10.2 shows a 20 Ω resistor connected to a power supply.

A second 20 Ω resistor is connected in series with the first.

State and explain how this affects the current in the circuit.

A teacher is investigating the resistance of a lamp.

Fig. 10.1 shows part of the circuit she uses. The circuit is incomplete.

(i) To determine the resistance of the lamp, the teacher adds two meters to her circuit.

On Fig. 10.1, draw circuit symbols to show each meter correctly connected in the circuit.

[3]

(ii) When the current in the lamp is 0.25A, the potential difference (p.d.) across the lamp is 4.5 V. Calculate the resistance of the lamp.

resistance = ...................................................... Ω [3]

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(i) State the name of component X.

[1]

(ii) Describe and explain how the teacher uses component X to investigate the resistance of the lamp.

[2]

A teacher uses a power supply in a metal case. The circuit for the power supply includes a fuse.

(i) Draw the electrical symbol for a fuse.

[1]

(ii) The metal case of the power supply is earthed. A fault occurs and a live wire touches the metal case.

 Explain how earthing the metal case protects the teacher.

[3]

The power supply circuit includes a transformer. Its input voltage is 240 V. There are 960 turns on the input coil and 64 turns on the output coil.

Calculate the output voltage of the transformer.

output voltage = ..................................................... V 

A circuit is made from two lamps, a cell and a switch, as shown in Fig. 10.1.

(i) Draw the circuit symbol for a cell.

[1]

(ii) State the term used for the arrangement of lamps in the circuit in Fig. 10.1.

[1]

(iii) The switch is closed and the lamps light.

State the name of the charged particles that are flowing through the wires.

[1]

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Fig. 10.2 represents a different type of circuit.

(i) Compare Fig. 10.1 and Fig. 10.2.

State two advantages of the type of circuit shown in Fig. 10.2 with the type of circuit shown in Fig. 10.1.

[2]

(ii) The potential difference across the power source in Fig. 10.2 is 3.0 V. The combined resistance of the two lamps is 12 Ω.

 Calculate the size of the current in the circuit when the switches are closed.

current = ...................................................... A [3]

Fig. 11.1 shows lamps in series. Fig. 11.2 shows lamps in parallel.

The lamps are all identical 6.0 V lamps. In each circuit there are three ammeters A₁, A₂ and A₃.

(i) Compare the readings on ammeters A₁, A₂ and A₃ in Fig. 11.1.

[1]

(ii) Compare the readings on ammeters A₁, A₂ and A₃ in Fig. 11.2.

[1]

(ii) State two advantages of connecting the 6.0 V lamps in parallel with the 6.0 V battery, compared with connecting the lamps in series with the battery.

[2]

Each lamp has a resistance of 12 Ω.

(i) Determine the combined resistance of the two lamps connected in series.

resistance = .................................................... Ω [1]

(ii) Compare the resistance of one lamp with the combined resistance of the two lamps in parallel.

[1]

Fig. 8.1 shows a circuit.

The lamp has a resistance of 3.0 Ω. Line XY represents a uniform resistance wire of resistance 6.0 Ω.

  Calculate the reading on the ammeter.

  ammeter reading = ........................................................ 

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Fig. 8.2 shows the circuit with a different connection to the resistance wire and an added resistor.

The length XY of the whole resistance wire is 2.0 m. The contact is made at Q where the distance XQ is 0.60 m.

Calculate the resistance of the circuit.

   resistance = ........................................................

A teacher demonstrates the action of a device. Fig. 10.1 shows the symbol for the device.

State the name of this device.

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Fig. 10.2 shows another device being used in a circuit. The circuit contains a 6.0 V lamp.

(i) The sliding contact of this device is at position A, as shown in Fig. 10.2.

    Describe and explain the brightness of the lamp when the sliding contact is in this position.

[2]

(ii) The teacher moves the sliding contact from position A to position B. Describe and explain what happens to the brightness of the lamp.

[2]

(iii) The teacher moves the sliding contact from position B to position C. Suggest what happens to the lamp.

[1]

Fig. 8.1 shows a circuit that contains a battery of electromotive force (e.m.f.) 6.0 V, an ammeter, a 20 Ω resistor and component X.

(i) State the name of component X.

[1]

(ii) The potential difference (p.d.) across the 20 Ω resistor is measured with a voltmeter.

  On Fig. 8.1, draw the symbol for this voltmeter connected to the circuit.

[1]

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The p.d. across the 20 Ω resistor is varied from zero to 6.0 V. For each value of p.d. a corresponding current is measured.

On Fig. 8.2, draw a line to indicate how the current measured by the ammeter depends on the p.d. across the 20 Ω resistor.

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A second resistor is connected to the circuit in parallel with the 20 Ω resistor. 

(i) State how the combined resistance of the two resistors in parallel compares with the resistance of each of the resistors on its own.

[1]

(ii) The p.d. across the two parallel resistors is changed and the current in the battery for each value of the p.d. is measured. A second line could be drawn on Fig. 8.2 to indicate how the current measured by the ammeter depends on the p.d. across the two resistors in parallel.

State how the second line differs from the original line. You are not expected to draw this second line.

[1]

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The circuit shown in Fig. 1 includes three ammeters labelled A₁, A₂ and A₃, and one unknown fixed resistor, R.

The voltmeter connected across R reads 24 V.

For the parallel branch, determine     

(i) the voltage across the upper 10 Ω resistor.

[2]

(ii) the voltage across the lower part of the parallel circuit.

[1]

Calculate the current through the upper 10 Ω resistor.

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Determine the readings on

(i) ammeter A₂

[2]

(ii) ammeters A₁ and A₃.

[2]

Calculate the value of R.